Micro-actuation element provided with torsion bars

ABSTRACT

The micro-actuation element (X 1 ) includes a movable unit ( 111 ), a frame ( 112 ) and a coupler ( 113 ) for connecting these, where the unit, the frame and the coupler are integrally formed in a material substrate having a multi-layer structure that consists of electroconductive layers ( 110   a - 110   c ), such as a core conduction layer ( 110   b ), and insulation layers ( 110   d,    110   e ) intervening between the electroconductive layers ( 110   a - 110   c ). The movable unit ( 111 ) includes a first structure originating in the core conduction layer ( 110   b ). The frame ( 112 ) includes a second structure originating in the core conduction layer ( 110   b ). The coupler ( 113 ) includes a plurality of electrically separated torsion bars ( 113   a,    113   b ) that originate in the core conduction layer ( 110   b ) and are connected continuously to the first structure and the second structure.

TECHNICAL FIELD

The present invention relates to a micro-actuation element provided withtorsion bars. In particular, the present invention is a micro-mirrorelement used to change the direction of light progression by means ofoptical reflection, the element being built into a device such as anoptical switching device which switches the light path among multipleoptical fibers, and an optical disk device which accomplishes storageand playback processing of data onto an optical disk.

BACKGROUDN ART

In recent years, optical communication technology has come to be broadlyused in a variety of fields. In optical communications, optical signalsare transmitted using optical fibers as a medium. In order to switch theoptical signal transmission path from one fiber to another, generallyuse is made of a so-called optical switching device. In achieving goodoptical communication, as the properties sought for optical switchingand the switching operation, there is a need for optical devices havinglarge capacity, high-speed, and high reliability. From this perspective,as optical switching devices, there is heightened expectation relatingto the combining micro-mirror elements manufactured by micromachiningtechnology. By means of a micro-mirror element, switch processing can beaccomplished between the input side optical transmission path and theoutput side optical transmission path in an optical switching device,using an optical signal in its existent state, without converting theoptical signal to an electric signal, which is desirable in obtainingthe above-noted properties.

The micro-mirror element is provided with a mirror surface to reflectlight, which enables changing the direction of the light reflection byoscillating the mirror surface. Micro-mirror elements of the staticelectricity drive type which use electrostatic power to oscillate themirror surface is used by many optical devices. A electrostatic drivemicro-mirror element can be largely classified into two types, that is,a micro-mirror element manufactured by so-called surface micromachiningtechnology and a micro-mirror element manufactured by so-called bulkmachining technology.

With surface micromachining technology, a thin film materialcorresponding to each of the construction members is processed onto asubstrate in a desired pattern, and by successively accumulating such apattern, formation is accomplished of each of the members constructingelements such as a support body, a mirror surface and an electrode andthe like, or a subsequently removed sacrificial layer. A electrostaticdrive type micro-mirror element constructed by this type of surfacemicromachining technology is disclosed, for example, in JP-A-H07-287177.

On the other hand, with bulk micromachining technology, by etching thematerial substrate itself, a support body or mirror and the like can beformed into a desired shape, and the mirror surface or electrode can beformed into a thin film, in accordance with the need. The electrostaticdrive type micro-mirror element manufactured by such bulk micromachiningtechnology is disclosed, for example, in JP-A-H09-146032,JP-A-H09-146034, JP-A-H10-62709, and JP-A-2001-13443.

As one of the technical items required in a micro-mirror element, amirror surface should have a high degree of flatness, to ensure lightreflection. By means of surface micromachining technology, since thesurface of a finally formed mirror is thin, the mirror surface is easilybent, and in assuring a high degree of flatness, the size of the mirrorsurface need have a length of several 10 μm.

On the other hand, according to bulk micromachining technology, a mirrorportion is formed by subjecting a relatively thick material substrate toetching, and then a mirror surface is provided on this mirror portion.In this manner, even with a mirror surface having a wide surface area,rigidity can be assured. As a result, it becomes possible to form amirror surface provided with a sufficiently high degree of opticalflatness. Therefore, particularly with the construction of amicro-mirror element in which the mirror surface of the length of oneborder must be 100 μm or greater, bulk micromachining technology iswidely adopted.

FIG. 18 and FIG. 19 show a conventional static drive type micro-mirrorelement 400 manufactured by means of bulk micromachining technology.FIG. 18 is an exploded perspective view of micro-mirror element 400, andFIG. 19 is a cross-sectional view taken along the line XIX-XIX of FIG.18 in a micro-mirror element 400 in the assembled state. Micro-mirrorelement 400 has construction in which the mirror substrate 410 and thebase substrate 420 form cumulative layers. The mirror substrate 410 isformed from a set of torsion bars 413 which connect the mirror 411 withthe frame 412. Relative to a specific material substrate comprised of asilicon substrate and the like which has conductive characteristics, byetching from one of its sides, formation can be accomplished of theouter contour of a mirror 411, a frame 412 and a set of torsion bars413. To the surface of the mirror component 411 is attached a mirrorsurface 414. To the rear surface of the mirror 411 is attached a set ofelectrodes 415 a and 415 b. To the base substrate 420 is attached anelectrode 421 a which faces the electrode 415 a of the mirror 411, andan electrode 421 b which faces the electrode 415 b.

In the micro-mirror element 400, if an electric potential is applied toframe 412 of the mirror substrate 410, it is generally formed with thesame conductive material as that of the frame 412. Electric potential istransmitted to the electrode 415 a an electrode 415 b through the set oftorsion bars 413 and mirror 411. Furthermore, by applying a specificelectric potential to the frame 412, electrification can ordinarily beaccomplished, for example, of electrodes 415 a and 415 b. In this state,if a negative electric charge is applied to electrode 421 a of the basesubstrate 420, then electrostatic attraction is generated between theelectrode 415 a and electrode 421 a, and while twisting a set of torsionbars 413, the mirror 411 rotates in the direction of the arrow M1. Ifthe mirror 411 vibrates until the sum of the twist resistance force ofthe torsion bars 413 and the electrostatic attraction between theelectrodes reaches a point of equilibrium, then it stands still.

Instead of this, in a state in which the electrode 415 a and theelectrode 415 b of the mirror 411 is positively charged, if a negativecharge is applied to the electrode 421 b, static attraction is generatedbetween the electrode 415 b and the electrode 421 b, and the mirror 411vibrates in a direction reverse of that of the arrow M1, and settlesdown. By means of the oscillating drive of the mirror 411, thereflection direction of the light reflected by the mirror surface 414 isswitched.

In the micro-mirror element 400, however, the driving of the mirror 411,i.e., movable member, is performed by the application of only oneelectric potential. Specifically, if electric potential is applied toframe 412 of the mirror substrate 410, then the electric potential istransmitted to the mirror 411 through the set of torsion bars 413, andthe mirror and 411 and the attached electrodes 415 a and 415 b come tohave the same electric potential. In micro-mirror element 400, theapplication of different electric potential cannot be applied to theelectrodes 415 a and 415 b to drive the movable unit. Owing to this,with the micro-mirror element 400, since the degree of freedom is lowrelative to the driving state of the movable unit, there is difficultyin realizing complex operations with the movable member. Theconventional micro-mirror element 400 may fail to meet the requirementsfor an optical switching element built into an optical communicationsdevice, for example.

DISCLOSURE OF THE INVENTION

The present invention has been proposed under the circumstancesdescribed above, and therefore its object is to provide amicro-actuation element capable of realizing complex operations at itsmovable unit.

According to a first aspect of the present invention, there is provideda micro-actuation element, which includes a movable unit, a supportframe and a coupler for connecting the unit and the frame. The unit, theframe and the coupler are integrally formed in a material substrate witha multi-layer structure comprising a plurality of electroconductivelayers and insulation layers arranged between the electroconductivelayers. The electroconductive layers include a core conduction layer.The movable unit comprises a first structure originating in the coreconduction layer. The frame comprises a second structure originating inthe core conduction layer. The coupler comprises a plurality ofelectrically separated torsion bars originating in the core conductionlayer and continuously connected to the first structure and the secondstructure. According to the present invention, with respect to themovable unit and the frame, some arrangements originating in the sameelectroconductive layer are to be considered as providing a singlestructure, even if they are physically separated into several sections.Thus, in the movable unit, the first structure originating in the coreconduction layer serves as a single assembly, if it consists ofphysically separated sections. Likewise, in the frame, the secondstructure serves as a single assembly.

The micro-actuation element having such construction is able to realizecomplex operations in the movable unit. The micro-actuation elementaccording to the first aspect of the present invention is an elementformed in a material substrate which has multi-layer construction,accomplished by a bulk micromachining technology such as MEMS(Micro-Electro-Mechanical Systems). The first construction of themovable unit, the second construction of the frame and the multipletorsion bars of the coupler continuously connected to these originate ina single conduction layer, namely, the core conduction layer. At thesame time, the multiple torsion bars included in the single coupler aremutually electrically separated. Also, in the first construction and thesecond construction to which these are connected is formed with aconduction path in which there is no short-circuiting between themultiple torsion bars. Thus, in the micro-actuation element of the firstaspect, it is possible for the transmission of multiple electricpotentials to be connected from the frame to the movable unit through asingle coupler.

For example, a first torsion bar selected from the multiple torsion barsmay be connected to a first part of the first structure in the movableunit and to a first part of the second structure in the frame, while asecond torsion bar selected from the multiple torsion bars may beconnected to a second part of the first structure and to a second partof the second structure. In such an instance, different electricpotentials can be transmitted from the frame to the movable unit via asingle coupler.

Specifically, when electric potential is applied to the first part ofthe second construction, then electric potential is transmitted to thefirst part of the first construction through the first torsion bar, butis not transmitted to the second torsion bar nor the the second part ofthe first construction to which the second torsion bar is connected. Onthe other hand, when electric potential is applied to the second part ofthe second construction, then the electric potential is transmitted tothe second part of the first construction through the second torsionbar, but is not transmitted to the first torsion bar nor the first partof the first construction to which the first torsion bar is connected.

In this manner, in the micro-actuation element according to the firstaspect of the present invention, multiple electric potentials can betransmitted, and it is possible to apply multiple electric potentialsrelative to the multiple parts of the movable unit. Thus, themicro-actuation element according to the first aspect has a degree offreedom with respect to the rotation of the movable unit around the axisdefined by the coupler, and it is possible to realize complex operationsin the movable unit. This type of micro-actuation element can be appliedto built-in high-performance devices.

Preferably, the coupler includes two torsion bars offset in the widthwise direction. The spacing of the two torsion bars is greater as thebars are closer to the movable unit. More preferably, when the spacingin the frame is Wf, the spacing in the movable unit is Wm, and theoffset distance of the movable unit and the frame in the disposedlocation of the coupler is L, then the following inequalities 0<Wf<L andWf<Wm<Wf+4L are satisfied. With such an arrangement, it is possible tosuppress inappropriate movement of the movable unit such as rotation ofthe movable unit in a virtual plane parallel to the rotational axisdefined by the coupler.

In a micro-actuation element such as a micro-mirror element, it is oftennecessary to make the twist resistance of the coupler or torsion bars assmall as possible. In order to set a low twist resistance of thecoupler/torsion bar, conventionally the width or thickness of thetorsion bar is made small. For example with the micro-mirror element 400shown in FIG. 18 or 19, in order to reduce the twist resistance of thetorsion bar 413, the width d1 or the thickness d2 of the torsion bar 413is made small. However, by only making the width d1 or the thickness ofthe torsion bar 413 small, rotation of the mirror 411 around the normalN4 of the mirror surface 414 can occur. This being the case, in drivingthe mirror 411, not only the suitable rotation around the rotating axisA5 defined by the torsion bars 413, but also rotation around the normalN4 may occur. This obstructs precise control of the micro-mirror element400.

According to the preferred embodiment of the present invention, thespacing of the two torsion bars of the coupler becomes larger as thebars are closer to the movable unit. Therefore even in the case wherethe thickness or width of each torsion bar is made small for reducingthe twist resistance in the coupler, the inappropriate movement of themovable unit, such as rotation in a virtual plane parallel to thecoupler-defined rotating axis, can be appropriately suppressed.

According to the first aspect of the present invention, the movable unitmay include a movable core portion, a relay frame connected to theabove-mentioned support frame through the coupler, and a relay couplerwhich connects the movable core portion and the relay frame. In thiscase, preferably the movable core portion may include a thirdconstruction which originates in the core conduction layer, the relayframe may include a first construction, and the relay coupler mayinclude a plurality of electrically separated torsion bars thatoriginate in the core conduction layer and are continuously connected tothe third construction and the first construction. Further, the relaycoupler may preferably include two relay torsion bars spaced from eachother in the width wise direction, the spacing of the two relay torsionbars being greater as the bars are closer to the movable core portion.The micro-actuation element of the present invention may be constructedas a dual axis type.

In a preferred embodiment of the micro-actuation element according tothe first aspect of the present invention, the movable unit is providedwith a first comb-tooth electrode, and the frame is provided with asecond comb-tooth electrode for moving the movable unit by generatingstatic electricity between the first comb-tooth units. In case ofconstructing the dual axis type, the movable core portion is providedwith another first comb-tooth electrode and the relay frame is providedwith another second comb-tooth electrode for moving the movable coreportion by electrostatic force generated in cooperation with the firstcomb-tooth electrodes. Driving the movable unit by means of comb-toothelectrode is preferable for controlling the movable unit with highprecision. In another preferable embodiment, the micro-actuation elementis further provided with a base facing the movable unit, the base beingprovided with a flat electrode facing the mirror. In this case, themovable unit may be provided with a flat electrode facing the flatelectrode formed on the base. In another preferable embodiment, themicro-actuation element is further provided with a base which faces themovable unit, wherein a first magnetic coil is attached to the movableunit, and the base is provided with a magnetic coil or a magnet formoving the movable unit by electromagnetic force generated incooperation with the first magnetic coil. In another preferableembodiment, a micro-actuation element is further provided with a basewhich faces the movable unit, wherein a magnet is attached to themovable unit, and the base is provided with an electromagnetic coil formoving the movable unit by electromagnetic force generated incooperation with the magnet.

Preferably, the movable unit further includes a third construction whichoriginates in the conduction layer connected to the core conductionlayer through an insulation layer in the material substrate. At least apart of the third construction and a part of the first construction areelectrically connected to each other by a conduction plug which passesthrough the intervening insulation layer. Such an arrangement isadvantageous to realize proper formation of a conduction path in themovable unit.

Preferably the frame further includes a third construction whichoriginates in the conduction layer connected to the core conductionlayer through the insulation layer in a material substrate. At least apart of the third construction and a part of the second construction areelectrically connected to the conduction plug which passes through theintervening insulation layer. Such an arrangement is advantageous torealize proper formation of a conduction path in the frame.

Preferably, the micro-actuation element includes a mirror provided onthe movable unit for serving as a micro-mirror element.

According to a second aspect of the present invention, there is provideda micro-actuation element. This micro-actuation element includes amovable unit, a frame and a coupler for connecting the unit and theframe, wherein the unit, the frame and the coupler are integrally formedin a material substrate having a multi-layer structure that includes afirst electroconductive layer, a second electroconductive layer, a thirdelectroconductive layer, a first insulation layer intervening betweenthe first and the second electroconductive layers, and a secondinsulation layer intervening between the second and the thirdelectroconductive layers. The movable unit includes a first structureoriginating in the second electroconductive layer. The frame includes asecond electroconductive layer originating in the secondelectroconductive layer. The coupler includes a plurality ofelectrically separated torsion bars that originate in the secondelectroconductive layer and are connected continuously to the first andthe second structures.

The above-described micro-actuation element incorporates the features ofthe micro-actuation element according to the first aspect of the presentinvention. Thus, according to the second aspect of the presentinvention, the same advantages as those described above with respect tothe first aspect can be enjoyed with the micro-actuation element, whichis integrally formed in the multi-layered material substrate made up ofa first electroconductive layer, a second electroconductive layer, athird electroconductive layer, a first insulation layer and a secondinsulation layer.

According to the second aspect, preferably, the movable unit includes athird construction which originates in the first conduction layer, andat least a part of the third construction and a part of the firstconstruction are electrically connected by means of a conduction plugpassing through the intervening first insulation layer. Such anarrangement is advantageous to realize proper formation of a conductionpath in the movable unit.

Preferably, the movable unit includes a movable core portion, a relayframe connected to the support frame by the coupler, and a relay couplerconnecting the movable core portion and the relay frame. The movablecore portion includes a third structure originating in the firstelectroconductive layer and a fourth structure originating in the secondelectroconductive layer. At least a part of the third structure and atleast a part of the fourth structure are connected to each other by afirst conduction plug passing through the first insulation layerintervening between the third and the fourth structures. The relay framefurther includes a fifth structure originating in the firstelectroconductive layer, the first structure originating in the secondelectroconductive layer and a sixth structure originating in the thirdelectroconductive layer. At least a part of the fifth structure and apart of the first structure are connected to each other by a secondconduction plug passing through the first insulation layer interveningbetween the fifth and the first structures. Another part of the firststructure and at least a part of the sixth structure are connected toeach other by a third conduction plug passing through the secondinsulation layer intervening between the first and the sixth structures.The relay coupler includes a plurality of electrically separated torsionbars that originate in the second electroconductive layer and areconnected continuously to the fourth structure and the first structure.Such an arrangement is advantageous to realize proper formation of aconduction path in the movable unit of a dual axis micro-actuationelement.

Preferably, the frame may further include a third structure originatingin the first electroconductive layer and a fourth structure originatingin the third electroconductive layer. At least a part of the thirdstructure and a part of the second structure are connected to each otherby a first conduction plug passing through the first insulation layerintervening between the third and the second structures. Another part ofthe second structure and at least a part of the fourth structure areconnected to each other by a second conduction plug passing through thesecond insulation layer intervening between the second and the fourthstructures. Such an arrangement is advantageous to realize properformation of a conduction path in the frame.

According to a third aspect of the present invention, there is provideda micro-actuation element. This micro-actuation element includes amovable unit, a frame and a coupler connecting these. The unit, theframe and the coupler are integrally formed in a material substratehaving a multi-layer structure that includes a first electroconductivelayer, a second electroconductive layer, a third electroconductivelayer, a first insulation layer arranged between the first and thesecond electroconductive layers, and a second insulation layer arrangedbetween the second and the third electroconductive layers. The movableunit includes a first structure originating in the firstelectroconductive layer, a second structure originating in the secondelectroconductive layer and a third structure originating in the thirdelectroconductive layer. At least a part of the first structure and afirst part of the second structure are connected to each other by afirst conduction plug passing through the first insulation layerintervening between the first and the second structures. A second partof the second structure and at least a part of the third structure areconnected to each other by a second conduction plug passing through thesecond insulation layer intervening between the second and the thirdstructures. The frame includes a fourth structure originating in thefirst electroconductive layer, a fifth structure originating in thesecond electroconductive layer and a sixth structure originating in thethird electroconductive layer. At least a part of the fourth structureand a first part of the fifth structure are connected to each other by athird conduction plug passing through the first insulation layerintervening between the fourth and the fifth structures. A second partof the fifth structure and at least a part of the sixth structure areconnected to each other by a fourth conduction plug passing through thesecond insulation layer intervening between the fifth and the sixthstructures. The coupler includes a first torsion bar that originates inthe second electroconductive layer and is connected continuously to thefirst part of the second structure and the first part of the fifthstructure. The coupler also includes a second torsion bar thatoriginates in the second electroconductive layer and is connectedcontinuously to the second part of the second structure and the secondpart of the fifth structure.

The above-described micro-actuation element includes the features of themicro-actuation element according to the first aspect of the presentinvention. Thus, the same advantages as those described above withrespect to the first aspect can be enjoyed with the element of the thirdaspect.

Specifically, according to the third aspect of the present invention,when electric potential is applied to at least a part of the fourthconstruction in the frame, then the electric potential is applied to atleast a part of the first structure in the movable unit via the thirdconduction plug, the first part of the fifth structure, the firsttorsion bar, the first part of the second structure in the movable unit,and the first conduction plug. Likewise, when electric potential isapplied to at least a part of the sixth construction in the frame, thenthe electric potential is applied to at least a part of the thirdconstruction in the movable unit by the fourth conduction plug, thesecond part of the fifth construction, the second torsion bar, thesecond part of the second construction in the movable unit, and thesecond conduction plug.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a micro-mirror element according toa first embodiment of the present invention.

FIG. 2 is an exploded view of the micro-mirror element shown in FIG. 1.

FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2.

FIG. 4 is a cross-sectional view taken along the line in IV-IV FIG. 2.

FIG. 5 is an enlarged plan view of part of the micro-mirror elementshown in FIG. 1.

FIG. 6 is a perspective view showing a micro-mirror element according toa second embodiment of the present invention.

FIG. 7 is an exploded view of the micro-mirror element shown in FIG. 6.

FIG. 8 is a cross-sectional view taken along the line VIII-VIII of FIG.7.

FIG. 9 is a cross-sectional view taken along the line IX-IX of FIG. 7.

FIG. 10 is a perspective view showing a micro-mirror element accordingto a third embodiment of the present invention.

FIG. 11 is an exploded plan view of the micro-mirror element shown inFIG. 10.

FIG. 12 is a cross-sectional view of part of the micro-mirror elementshown in FIG. 10.

FIG. 13 is a cross-sectional view of another part of the micro-mirrorelement shown in FIG. 10.

FIG. 14 is a cross-sectional view of another part of the micro-mirrorelement shown in FIG. 10.

FIG. 15 is a cross-sectional view of another part of the micro-mirrorelement shown in FIG. 10.

FIG. 16 is a cross-sectional view of another part of the micro-mirrorelement shown in FIG. 10.

FIGS. 17 a-17 e show variations of conduction plugs.

FIG. 18 is a perspective view showing a conventional micro-mirrorelement.

FIG. 19 is a cross-sectional view taken along the line XIX-XIX of FIG.18.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 and FIG. 2 show a micro-mirror element X1 according to a firstembodiment of the present invention. Micro-mirror element X1 hasconstruction in which a mirror substrate 110 and a base substrate 120are accumulated.

Mirror substrate 110, as shown in FIG. 1, is provided with a mirror 111and a frame 112 which encloses the mirror 111, and couplers 113 whichconnect the frame 112 and the mirror 111. The mirror substrate 110 isformed in a multi-layer material substrate by e.g. a bulk micromachiningtechnology such as MEMS technology. The material substrate is providedwith multi-layer construction formed from a first silicon layer 110 a, asecond silicon layer 110 b, and a third silicon layer 110 c as well as afirst insulation layer 100 d provided between the silicon layers, and asecond insulation layer 110 e, in which conductive characteristics areapplied by doping an n type impurity of P or As; or a p type impurity ofB and like. Multi-layer construction is shown in FIG. 3 and FIG. 4. Thethickness of the first silicon layer 110 a and the thickness of thethird silicon layer 110 c is, for example, 100 μm, and the thickness ofthe second silicon layer 110 b is, for example, 5 μm. The firstinsulation layer 110 d and the second insulation layer 110 e are, forexample, provided with a thickness of 1 μm formed from oxidized silicongrown by means of the heat oxidation method on any of the first throughthird silicon layers 100 athrough 110 c . The material substrate isappropriately multi-layered in the formation process of the mirrorsubstrate 110.

In the formation of the mirror substrate 110, use is made of severaletching masks, depending on the multi-layer structure of the materialsubstrate, such as an etching mask for covering a part corresponding tothe mirror 111, an etching mask for covering a part corresponding to theframe 112, and an etching mask for covering parts corresponding to thepaired couplers 113. Then, each silicon layer is processed by the DeepRIE (Deep Reactive Ion Etching) method such as Si etching, or by KOH wetSi etching. Unnecessary members in the insulation layer are removed byetching. As a result, in the mirror substrate 110, formation isaccomplished of a mirror 111, a frame 112, and a set of couplers 113. Inthe illustrated example, the distance between the mirror 111 and theframe 112, is for example, 10-200 μm.

The mirror 111, as is shown in FIG. 2, is provided with an upper layer111 a, and lower layers 111 b and 111 c. The upper layer 111 aoriginates in the first silicon layer 110 a, and the lower layers 111 band 111 c originate in the second silicon layer 110 b. Between the upperlayer 111 a and the lower layers 111 b and 111 c there is an interveningfirst insulation layer 110 d. In FIG. 2, the first insulation layer 110d is depicted by cross hatching on a member originating in the secondsilicon layer 110 b of the mirror substrate 110.

To the upper layer 111 a of the mirror 111 is attached a mirror surface114 used for optical reflection. The lower layers 111 b and 111 c arerespectively formed with electrodes 115 a and 115 b. Mirror surface 114and electrodes 115 a and 115 b are formed by the vapor deposition of ametallic film. However, in the case where conductivity of the secondsilicon layer is made to be adequately high by doping impurities,electrodes 115 a and 115 b need not be used.

As shown in FIG. 2, Frame 112 is provided with an upper layer 112 a,middle layers 112 b and 112 c and a lower layer 112 d. The upper layer112 a originates in the first silicon layer 110 a, and the middle layers112 b and 112 c originate in the second silicon layer 110 b, and thelower layer 112 d originates in the third silicon layer 110 c. Betweenthe upper layer 112 a and the middle layers 112 b and 112 c, as seen inFIGS. 2-4, is an intervening first insulation layer 110 d. Between themiddle layers 112 b, 112 c and the lower layer 112 c is an interveningsecond insulation layer 110 e. In FIG. 2, the second insulation layer110 e is depicted by cross hatching on a member originating in the thirdsilicon layer 110 c of the mirror substrate 110.

In the frame 112, the upper layer 112 a and the middle layers 112 b, asseen in FIG. 3, are electrically connected by two plugs 116 which passthrough the first insulation layer 110 d. Each of the plugs 116 isformed, for example, from polysilicon filled between the upper layer 112a and the middle layer 112 b. The middle layer 112 c and the lower layer112 d, as shown in FIG. 4, are electrically connected by two plugs 117which pass through the second insulation layer 110 e. Each of the plugs117 is formed, for example, from polysilicon filled between the middlelayer 112 c and the lower layer 112 d.

Each coupler 113 connects the mirror 111 and the frame 112 to eachother. The micro-mirror element X1 is constructed as a single axis typein which the movable unit or mirror 111 has only one rotating axis A1defined by a pair of couplers 113. In the illustrated example, eachcoupler 113 consists of two torsion bars 113 a, 113 b spaced from eachother.

As seen in FIG. 2, the torsion bar 113 a, originating in the secondsilicon layer 110 b, is formed integral with the lower layer 111 b ofthe mirror 111 and with the middle layer 112 b of the frame 112. Inother words, the torsion bar 113 a is continuously connected to thelower layer 111 b and the middle layer 112 b. Likewise, the torsion bar113 b, originating in the second silicon layer 110 b, is formed integralwith the lower layer 111 c of the mirror 111 and with the middle layer112 c of the frame 112. In other words, the torsion bar 113 b iscontinuously connected to the lower layer 111 c and the middle layer 112c.

The two torsion bars 113 a, 113 b determines the width of the coupler113 (the measurement in the Y direction in FIG. 1). Spacing between thetwo torsion bars 113 a and 113 b becomes larger as the bars are closerto the mirror 111, but gradually becomes smaller as closer to the frame112 a. As seen in FIG. 5, if spacing between the two torsion bars 113 a,113 b in frame 112 is Wf, the spacing in the mirror 111 is Wm, and theseparation distance between the mirror 111 and the frame 112 in thecoupler 113 is L, then the torsion bars 113 a and 113 b are so arrangedthat the relationship 0<Wf<L, and Wf<Wm<Wf+4L is satisfied. For example,if L is 100 μm then Wf is greater than 0 μm and less than 100 μm, and Wmis 100 μm or greater and less than 500 μm.

The base substrate 120 is constructed from, for example, anon-electroconductive silicon substrate. As shown in FIG. 2, a set offacing electrodes 121 a and 121 b are provided with appropriate spacingrelative to the set of electrodes 115 a and 115 b of mirror 111. Inother words, the micro-mirror element X1 is a so-called flat electrodetype. Electrodes 121 a and 121 b comprise a part of the pattern formedwiring (parts other than the electrode are abbreviated in the drawing)in base substrate 120.

In an assembled state of the micro-mirror element X1, the lower layer112 d of the frame 112 and the base substrate 120 are connected to eachother.

In the micro-mirror element X1, when a prescribed electric potential isapplied to the upper layer 112 a of the frame 112, then the electricpotential is transmitted to the electrode 115 a through the plug 116,middle layer 112 b, torsion bar 113 a and the middle layer 111 b ofmirror 111. In addition, when a prescribed electric potential is appliedto lower layer 112 d of the frame 112, then electric potential istransmitted to electrode 115 b through plug 117, middle layer 112 c,torsion bar 113 b and middle layer 111 c of mirror 111.

When the electric potential is applied to the electrode 115 a of themirror 111 and to the electrode 121 a of the base substrate 120,electrostatic attractive force and electrostatic repulsive force isgenerated between the electrode 115 a and the electrode 121 a. Likewise,when the electric potential is applied to the electrode 115 b of themirror 111 and to the electrode 121 b of the base electrode 120,electrostatic attractive force or electrostatic repulsive force isgenerated between the electrode 115 b and the electrode 121 b. By thecombined force of these electrostatic forces, the mirror 111 rotatesaround the rotating axis A1 while twisting the set of couplers 113.

In the micro-mirror element X1, by means of the above-described drivemechanism, the mirror 111, namely the movable unit, is driven, and themirror surface 114 can be faced in the desired direction. Accordingly,by means of the micro-mirror element 111, the reflection direction oflight reflected by the mirror surface 114 can be switched to the desireddirection.

In the micro-mirror element X1, the two torsion bars 113 a, 113 bincluded in a single coupler 113 are electrically separated from eachother. Further, the mirror 111 and the frame 112, to which these barsare connected, are formed with an electroconductive path arranged not togive rise to short-circuiting between the torsion bars 113 a and 113 b.Owing to this, in the micro-mirror element X1, multiple electricpotential can be transmitted relative to the mirror from the frame 112,so that different electric potentials are simultaneously applicable tothe mirror 111. As a result, the micro-mirror element X1 is providedwith a high degree of freedom of the rotating drive of the mirror 111around the rotating axis A1 defined by the coupler 113, whereby fineadjustment is possible for properly controlling the movement of themirror 111.

In addition, in the micro-mirror element X1, by constructing the coupler113 so that the torsion bars 113 a 113 b are sufficiently small, thetwist resistance of the coupler 113 is reduced. With a small amount oftwist resistance, the mirror 111 can be driven with a high degree ofprecision. At the same time, the pacing of the separated torsion bars113 a and 113 b in the width direction of the coupler 113 is such thatthe spacing Wm in the mirror 111 is greater than the spacing Wf in theframe 112. The coupler 113 having such construction is small in twistresistance, but effective in preventing the mirror 111 from rotatingaround the normal N1.

The mirror 111 of the micro-mirror element X1 may be driven byelectromagnetic force from an electromagnetic coil or permanent magnetin place of the electrostatic force caused by the flat electrodes.Specifically, the electrodes 115 a, 115 b of the mirror 111 may bereplaced by an electromagnetic coil, and the electrodes 121 a, 121 b ofthe base substrate may be replaced by an electromagnetic coil or apermanent magnet. Alternatively, the electrodes 115 a, 115 b of themirror 111 may be replaced by a permanent magnet, and the electrodes 121a, 121 b of the base substrate may be replaced by an electromagneticcoil. With this arrangement, the mirror 111 can be driven by adjustingthe state of electricity passing to the electromagnetic coil.

FIG. 6 and FIG. 7 show a micro-mirror element X2 according to a secondembodiment of the present invention. The micro-mirror element X2 isprovided with a mirror 211, a frame 212 encompassing the mirror 211, anda pair of couplers 213 connecting the frame 212 and the mirror 211 toeach other. The micro-mirror element X2 is formed in a material basesubstrate provided with multi-layered construction by means of the bulkmicromachining technology such as the MEMS technology. The materialsubstrate is provided with cumulative construction formed from a firstsilicon layer 210 a doped with n type impurities such as P and As or ptype impurities such as B for obtaining electroconductivity, a secondsilicon layer 210 b, and a third silicon layer 210 c, as well as a firstinsulation layer 210 d and a second insulation layer 210 e formedbetween the silicon layers. The multi-layer construction is shown inFIG. 8 and FIG. 9. The thickness of the first silicon layer 210 a is,for example, 10 μm, and the thickness of the second silicon layer 210 band the thickness of the third silicon layer 210 c are, for example, 100μm. The first insulation layer 210 d and the second insulation layer 210e are, for example, in any of the surfaces of the first -third siliconlayers 210 a-210 c, formed from oxidized silicon grown by theoxidization method, and have a thickness of 1 μm. The material substrateis made to be appropriately multi-layered in the formation process ofthe micro-mirror element X2.

In the formation of the micro-mirror element X2, use is made of etchingmasks, depending on the state of the cumulative construction in thematerial substrate, such as an etching mask for covering a partcorresponding to the mirror 211, an etching mask for covering a partcorresponding to the frame 212, and etching masks for covering partscorresponding to the paired couplers 213. Each silicon layer isprocessed by means of Si etching or KOH wet Si etching and the likeusing the Deep RIE method. Unnecessary portions in the insulation layerare etched away. As a result, the mirror 211, the frame 212, and the setof couplers 213 of the element X2 are formed. In the illustratedexample, the distance between the mirror 211 and the frame 212 is, forexample, 10-200 μm.

The mirror 211, as shown in FIG. 7, is provided with an upper layer 211,and lower layers 211 b and 211 c. The upper layer 211 a originates inthe first silicon layer 210 a. Lower layers 211 b and 211 c originate inthe second silicon layer 210 b. Between the upper layer 211 a and thelower layers 211 b, 211 c passes an intervening first insulation layer210 d. In FIG. 7, the first insulation layer 210 d is indicated by thecross-hatching on a portion originating in the second silicon layer 210b of the micro-mirror element X2.

To the upper layer mirror 211 a of the mirror 211 is attached a mirrorsurface 214 used for reflecting light. The mirror surface 214 is formedby vapor deposition of a metallic film, for example. The lower layers211 b, 211 c are provided with comb-tooth electrodes 215 a and 215 b,respectively. The comb-tooth electrodes 215 a and 215 b are respectivelya part of the middle layers 211 b and 211 c, and originate in the secondsilicon layer 210 b.

The frame 212, as shown in FIG. 7, is provided with upper layers 212a-212 b, middle layers 212 c-212 d, and lower layers 212 e-212 f. Theupper layers 212 a, 212 b originate in the first silicon layer 210 a;the middle layers 212 c, 212 d originate in the second silicon layer 210b, and the lower layers 212 e, 212 f originate in the third siliconlayer 210 c. Between the upper layers 212 a, 212 b and the middle layers212 c, 212 d, as seen in FIGS. 7-9, there is an intervening firstinsulation layer 210 d. Between the middle layers 212 c, 212 d and thelower layers 212 e, 212 f, there is an intervening second insulationlayer 210 e. In FIG. 7, the second insulation layer 210 e is indicatedby the cross-hatching on a portion originating in the third siliconlayer 210 c of the mirror element X2.

The lower layers 212 e, 212 f of the frame 212 are provided withcomb-tooth electrodes 216 a and 216 b, respectively. The comb-toothelectrodes 216 a and 216 b are respectively a part of lower layers 212 eand 212 f, and originate in the third silicon layer 210 c. In the frame212, the upper layer 212 a and the middle layer 212 c, as shown in FIG.8, are electrically connected to each other by two plugs 217 passingthrough the first insulation layer 210 d. The Plugs 217 are made, forexample, of polysilicon, and is formed to be filled in between the upperlayer 212 a and the middle layer 212 c. The upper layer 212 b and themiddle layer 212 d, as shown in FIG. 9, are electrically connected toeach other by two plugs 218 passing through the first insulation layer210 d. The plugs 218 is made, for example, of polysilicon, and is formedto be filled in between the upper layer 212 b and the middle layer 212d.

Each coupler 213 connects the mirror 211 and the frame 212 to eachother. The micro-mirror element X2 is constructed as a single axis typein which the movable unit or mirror 211 has one rotating axis A2 definedby a pair of couplers 213. In the illustrated example, each coupler 213consists of two torsion bars 213 a, 213 b separated from each other.

The torsion bar 213 a, originating in the second silicon layer 210 b andmade to be thinner than the second silicon layer 210 b, is formedintegral with the lower layer 211 b of the mirror 210 and the middlelayer 212 c of the frame 212. Likewise, the torsion bar 213 b,originating in the second silicon layer 210 b and made to be thinnerthan the second silicon layer 210 b, is formed integral with the lowerlayer 211 c of the mirror 211 and the middle layer 212 d of the frame212.

The two torsion bars 213 a, 213 b determines the width of the coupler213 (the measurement in the Y direction in FIG. 6). The spacing of thetwo torsion bars 213 a, 213 b becomes greater as the bars are closer tothe mirror 211, but gradually becomes smaller as the bars are closer tothe frame 212. Specific details are the same as those described abovewith reference to the torsion bars 113 a, 113 b of the micro-mirrorelement X1.

In the micro-mirror element X2 having such construction, when anelectric potential is applied to the upper layer 212 a of the frame 212,the electric potential is transmitted to the comb-tooth electrode 215 athrough the plugs 217, the middle layer 212 c, the torsion bars 213 aand the middle layer 211 b of the mirror 211. Likewise, when an electricpotential is applied to the upper layer 212 b of the frame 212, theelectric potential is transmitted to the comb-tooth electrode 215 bthrough the plugs 218, the middle layer 212 d, the torsion bars 213 band the middle layer 211 c of the mirror 211.

In the state in which electric potential is applied to the electrode 215a of the mirror 211, when the electric potential is applied to the lowerlayer 212 e of the frame 212 or to the comb-tooth electrode 216 a, thenelectrostatic attraction or repulsion is generated between thecomb-tooth electrode 215 a and the comb-tooth electrode 216 a. Likewise,in the state in which electric potential is applied to the comb-toothelectrode 215 b of the mirror 211, when the electric potential isapplied to the lower layer 212 f of the frame 212 or to the comb-toothelectrode 216 b, then electrostatic attraction or repulsion is generatedbetween the comb-tooth electrode 215 b and the comb-tooth electrode 216b. By means of the combined force of these electrostatic forces, themirror 211 rotates around the rotating axis A2 as twisting the couplers213.

In the micro-mirror element X2, the above-described drive mechanismactuates the mirror 211, namely the movable unit, thereby causing themirror surface 214 to face in the desired direction. Thus, according tothe micro-mirror element X2, it is possible to change the direction oflight reflected by the mirror surface 214, as required.

In the micro-mirror element X2, the two torsion bars 213 a, 213 bincluded in a single coupler 213 are electrically separated from eachother. With the torsion bars 213 a, 213 b spaced from each other, themirror 211 and the frame 212, to which the torsion bars are connected,are provided with a conduction path in a manner such that noshort-circuiting occurs between the torsion bars 213 a and 213 b. Owingto this, in the micro-mirror element X2, it is possible to transmitmultiple electric potentials from the frame 212 to the mirror 211, andit is also possible to simultaneously transmit multiple electricpotentials to the mirror 211. With such an arrangement, the micro-mirrorelement X2 is provided with a high degree of freedom relative to thestate of rotational driving of the mirror 211 around the rotating axisA2 defined by the coupler 213, whereby complex operations with respectto the mirror 211 can be realized.

As described above with respect to the coupler 113 of the mirror elementX1, the coupler 213 of the micro-mirror element X2 has a small twistresistance, while preventing the mirror 211 from unduly rotating aboutthe normal N2.

In the mirror element X2 described above, a pair of comb-toothelectrodes 215 a, 216 a and a pair of comb-tooth electrodes 215 a, 215 bare provided for driving the mirror 211 or the movable unit. With such acomb-tooth mechanism, it is possible to cause the working direction ofthe electrostatic force generated between the electrodes to be directedgenerally perpendicularly to the rotational direction of the mirror 211.In this manner, no attraction voltage (threshold voltage for causing asudden increase in the electrostatic force) occurs in driving the mirror211, whereby the mirror 211 can be tilted with a great inclinationangle. Advantageously, the comb-tooth electrodes are appropriate fordriving the movable unit with high precision.

FIG. 10 and FIG. 11 show a micro-mirror element X3 according to a thirdembodiment of the present invention. The micro-mirror element X3 isprovided with a mirror 310, an inner frame 320 surrounding the mirror310, an outer frame 330 surrounding the inner frame 320, a pair ofcouplers 340 connecting the mirror 310 and the inner frame 320 to eachother, and a pair of couplers 350 and 360 connecting the inner frame 320and the outer frame 330 to each other. The paired couplers 340 definethe rotating axis A3 of the rotational operation of the mirror 310relative to the inner frame 320. The couplers 350 and 360 define therotating axis A4 of the inner frame 320, and hence the mirror 310,relative to the outer frame 330. In the illustrated example, therotating axis A3 and the rotating axis A4 intersect at right angles.

The micro-mirror element X3 is formed in a multi-layer materialsubstrate by means of a bulk micromachining technology such as MEMS. Thematerial substrate has a multi-layer structure consisting of a firstsilicon layer 301, a second silicon layer 302, a third silicon layer303, a first insulation layer 304, and a second insulation layer 305,where the first to third silicon layers are made electroconductive bythe doping of an n-type impurity such as P and As, or a p-type impuritysuch as B, and where the first and second insulation layers are disposedbetween these silicon layers. The multi-layer structure of thisembodiment is shown in FIGS. 12-16. The first silicon layer 301 and thethird silicon layer 303 each have a thickness of 100 μm, for example.The second silicon layer 302 has a thickness of 5 μm, for example. Thefirst insulation layer 304 and the second insulation layer 305, eachhaving a thickness of 1 μm for example, are made of silicon oxide whichis grown on the first, the second or the third silicon layer 301-303 bythe thermal oxidation method. According to the present invention, thematerial substrate may be appropriately multi-layered in the formationprocessing of the micro-mirror element X3.

To produce the micro-mirror element X3, appropriate use is made of anetching mask which encompasses locations corresponding to the mirror310, and an etching mask which encompasses the location corresponding tothe inner frame 320, and an etching mask corresponding to the outerframe 330, as well as an etching mask which encompasses the locationscorresponding to the couplers 340, 350, and 360. Each of the siliconlayers are processed by, for example, Si etching accomplished by meansof the Deep RIE method, or the KOH wet Si etching. Nonessential portionsare etched away from the first insulation layer 304 and the secondinsulation layer 305. As a result, with the micro-mirror element X3,formation is accomplished of a mirror 310, an inner frame 320, an outerframe 330, and couplers 340, 350, and 360. In the present embodiment,the offset distance between the mirror 310 and the inner frame 320 andthe offset distance between the inner frame 310 and the outer frame 320is, for example, 10-200 μm.

The mirror 310, as shown in FIG. 11, is provided with an upper layer 311and four lower layers 312. FIG. 11 is an exploded plane surface diagramof the micro-mirror element X3. In FIG. 11, from the standpoint ofclarification, the construction originating in the second silicon layer302 is shown along with the construction originating in the firstsilicon layer 301 (shown by the broken line). The upper layer 311originates in the first silicon layer 301, and the lower layer 312originates in the second silicon layer 302. Between upper layer 311 andeach of the lower layers 312, as shown in FIG. 11 and FIG. 12, there isan intervening first insulation layer 304. In FIG. 11, the firstinsulation layer 304 is indicated by the cross-hatching on the portionoriginating in the second silicon layer 302 of the micro-mirror elementX3.

To the upper layer 311 of the mirror 310 is attached a mirror surface313 for light reflection. The mirror surface 313 is formed through thevapor deposition of metallic film, for example. The upper layer 311, atthe opposite ends thereof, is provided with a comb-tooth electrode 311 aand a comb-tooth electrode 311 b. The comb-tooth electrodes 311 a and311 b are a part of the upper layer 311 and originate in the firstsilicon layer 301.

In the mirror 310, the upper layer 311 and each lower layer 312, asshown in FIG. 12, are electrically connected to each other by means of aplug 310 a passing through the first insulation layer 304. The plug 310a is made, for example, of polysilicon, and formed to be filled betweenthe upper layer 311 and the lower layer 312.

As shown in FIG. 11, the inner frame 320 is provided with an upper layer321, four middle layers 323 a, 323 b, 324 a, 324 b, and lower layers325, 326. The upper layer 321 originates in the first silicon layer 301,and the middle layers 322, 323 a, 323 b, 324 a and 324 b originate inthe second silicon layer 302, and the lower layers 325 and 326 originatein the third silicon layer 303. As shown in FIGS. 11-16, there is afirst insulation layer 304 intervening between the upper layer 321 andeach of the middle layers 322, 323 a, 323 b, 324 a, 324 b. Likewise,there is a second insulation layer 305 intervening between the middlelayers 323 a, 323 b, 324 a, 324 b and the lower layers 325, 326. In FIG.11, the second insulation layer 305 is indicated by the cross-hatchingon a portion originating in the third silicon layer 303 of themicro-mirror element X3.

The upper layer 321 of the inner frame 320 is provided with comb-toothelectrodes 321 a and 321 b. The comb-tooth electrodes 321 a and 321 bare a part of the upper layer 321, and originate in the first siliconlayer 301. The lower layers 325 and 326 are respectively provided withcomb-tooth electrodes 325 a and 326 a. The comb-tooth electrodes 325 aand 325 b are a part of the lower layer 325 and 326, respectively, andoriginate in the third silicon layer 303. The comb-tooth electrodes 325a and 326 a are positioned downward of the comb-tooth electrodes 311 aand 311 b of the mirror 310, while also being arranged offset from thecomb-tooth electrodes 311 a and 312 a so as not to interfere with thecomb-tooth electrodes 311 a, 312 a when the mirror 310 rotates.

In the inner frame 320, as shown in FIG. 12, the upper layer 321 andeach of the middle layers 322, as shown in FIG. 12, are electricallyconnected to each other by means of the plug 320 a formed to be filledin between the upper layer 321 and the middle layer 322, passing throughthe first insulation layer 304. Likewise, the upper layer 321 and themiddle layer 323 a, as shown in FIG. 13, are electrically connected toeach other by means of the plug 320 b. Further, as shown in FIG. 14, theupper layer 321 and the middle layer 324 a are connected to each otherby means of the plug 320 c. The middle layer 323 b and the lower layer325, as shown in FIG. 15, are electrically connected to each other by aplug 320 d filled between the middle layer 323 b and the lower layer325, passing through the second insulation layer 305. In the samemanner, the middle layer 324 b and the lower layer 326, as shown in FIG.16, are electrically connected to each other by a plug 320 e. The plugs320 a-320 e are formed, for example, from polysilicon. Instead of theform of the plugs 320 a-320 c shown in FIG. 12-FIG. 14, formation may beaccomplished in the state shown in any of FIG. 17 a and FIG. 17 b. InFIG. 17 a, the plug (daubed black), made by using a separate plugmaterial, passes through the first silicon layer 301. In the exampleshown in FIG. 17 b, without using a separate material for a plug, theformation of the plug is accomplished in a manner such that a holeformed in the first insulation layer 304 is filled with the materialmaking the first silicon layer 301. Thus, the plug is formed in betweenthe first silicon layer 301 and the second silicon layer 302 forconnecting these layers to each other.

The outer frame 330, as shown in FIG. 11, is provided with an upperlayer 331, middle layers 332 a, 332 b, 333 a, 333 b, and lower layers334-338. The upper layer 331 originates in the first silicon layer 301,and the middle layers 332 a, 332 b, 333 a, and 333 b originate in thesecond silicon layer 302, and the lower layers 334-338 originate in thethird silicon layer 303. Between the upper layer 331 and each of themiddle layers 332 a, 332 b, 333 a and 333 b, as shown in FIGS. 11-16,there is an intervening first insulation layer 304. Between each of themiddle layers 332 a, 332 b, 333 a, 333 b and the lower layers 334-338,there is an intervening second insulation layer 305.

The lower layers 335 and 337 of the outer frame 330 are provided withcomb-tooth electrodes 335 a and 337 a, respectively. The comb-toothelectrodes 335 a and 337 a are a part of the lower layers 335 and 337,and originate in the third silicon layer 303. The comb-tooth electrodes335 a and 337 a are positioned below the comb-tooth electrodes 321 a and321 b of the inner frame 320, respectively, while also being arrangedoffset from the comb-tooth electrodes 321 a, 321 b so as not tointerfere with these electrodes when the inner frame 320 rotates.

In the outer frame 330, as shown in FIG. 13, the upper layer 331 and themiddle layer 332 a are connected to each other by a plug 330 a filledbetween the upper layer 331 and the middle layer 332 a, passing throughthe first insulation layer 304. In the same manner, the upper layer 331and the middle layer 333 a, as shown in FIG. 14, are electricallyconnected to each other by means of a plug 330 b passing through thefirst insulation layer 304. Further, the middle layer 332 b and thelower layer 336, as shown in FIG. 15, is electrically connected to eachother by means of a plug 330 c filled between the middle layer 332 b andthe lower layer 336, passing through the second insulation layer 305.Further, the middle layer 333 b and the lower layer 338, as shown inFIG. 16, are electrically connected to each other by means of a plug 330d. The plugs 330 a-330 d are formed, for example, from polysilicon.According to the present invention, instead of the shape shown in FIGS.12-14, any of the shapes shown in FIGS. 17 c-17 e may be formed for theplugs 320 d, 320 e. In the example shown in FIG. 17 c, a separate plugmaterial is used and formed into a plug (daubed black) passing throughthe third silicon layer 303. In the example shown in FIG. 17 d, withoutseparately using the plug material, a hole formed in the secondinsulation layer 305 is filled with the material making the secondsilicon layer 302, thereby producing the plug embedded in between thesecond silicon layer 302 and the third silicon layer 303 for connectingthese layers to each other. In the example shown in FIG. 17 e, noseparate plug material is used, but a cutout is formed in the secondinsulation layer 305, and then the second silicon layer 302 is formedfrom above the second insulation layer 305. Thus, a plug is formed toconnect the second silicon layer 302 and the third silicon layer 303.

Each coupler 340 connects the mirror 310 and the inner frame 320 to eachother. In the present embodiment, each of the couplers consists of twotorsion bars 341 spaced from each other.

The torsion bars 341, originating in the second silicon layer 302, areformed integral with the lower layer 312 of the mirror 310 and themiddle layer 322 of the inner frame 320, as shown in FIGS. 11 and 12.The two torsion bars 341 determine the width of the coupler 340, and thespacing of the two torsion bars 341 is greater as the bars are closer tothe mirror 310, but gradually becomes smaller as the bars are closer tothe frame 320. Specific details are the same as those described abovewith respect to the torsion bars 113 a, 113 b of the micro-mirrorelement X1.

Each of the couplers 350 connect the inner frame 320 and the outer frame330 to each other. With the present embodiment, each of the couplers 350consists of the mutually offset two torsion bars 351 and 352. Thetorsion bar 351 originates in the second silicon layer 302, and as shownin FIG. 11 and FIG. 13, is formed integral with the middle layer 323 aof the inner frame 320 and the middle layer 332 a of the outer frame330. The torsion bar 352 originates in the second silicon layer 302, andas shown in FIG. 11 and FIG. 15, is formed integral with the middlelayer 323 b of the inner frame 320 and the middle layer 332 b of theouter frame 330.

The two torsion bars 351, 352 determine the width of the coupler 350.The spacing of the two torsion bars 351, 352 becomes greater as the barsare closer to the inner frame 320, but gradually becomes smaller ascloser to the outer frame 330. Specific details are the same as thosedescribed above with reference to the torsion bars 113 a, 113 b of themicro-mirror element X1.

Each coupler 360 connects the inner frame 320 and the outer frame 330 toeach other. In the present embodiment, each coupler 360 consists of themutually offset two torsion bars 361 and 362. The torsion bar 361originates in the second silicon layer 302, and, as shown in FIG. 11 andFIG. 14, is formed integral with the middle layer 324 a of the innerframe 320 and the middle layer 333 a of the outer frame 330. The torsionbar 362 originates in the second silicon layer 302, and as shown in FIG.11 and FIG. 16, is formed integral with the middle layer 324 b of theinner frame letter 320 and the middle layer 333 b of the outer frame330.

The two torsion bars 361, 362 determine the width of the coupler 360.The spacing of the two torsion bars 361, 362 becomes greater as the barsare closer to the inner frame 320, but gradually becomes smaller ascloser to the outer frame 330. Specific details are the same as thosedescribed above with reference to the torsion bars 113 a, 113 b of themicro-mirror element X1.

In the above-described micro-mirror element X3, when an electricpotential is applied to the upper layer 331 of the outer frame 330, thepotential is transmitted to the upper layer 321 of the inner frame 320or to the comb-tooth electrodes 321 a, 321 b through the plug 330 ashown in FIG. 13, the middle layer 332 a of the outer frame 330, thetorsion bar 351, the middle layer 323 a of the inner frame 320, the plug32 b, and further through the plug 330 b shown in FIG. 14, the middlelayer 333 a of the outer frame 330, the torsion bar 361, the middlelayer 324 a of the inner frame 320, and the plug 320 c. Still further,this potential is transmitted to the upper layer 311 of the mirror 310or to the comb-tooth electrodes 311 a, 311 b through each plug 320 a,connected to the upper layer 321 as shown in FIG. 12, the torsion bar341 connected to the plug, the lower layer 312 of the mirror 310, andthe plug 310 a. Thus, when an electric potential is applied to the upperlayer 331 of the outer frame 330, then the electric potential istransmitted to the comb-tooth electrodes 311 a, 311 b and the comb-toothelectrodes 311 a, 311 b.

When applied to the lower layer 336 of the outer frame 330, the electricpotential is transmitted to the lower layer 325 of the inner frame 320or to the comb-tooth electrode 325 a through the plug 330 c shown inFIG. 15, the middle layer 332 b of the outer frame 330, the torsion bar352, the middle layer 323 b of the inner frame 320, and the plug 320 d.In the same way, when applied to the lower layer 338 of the outer frame330, the electric potential is transmitted to the lower layer 326 of theinner frame 320 or to the comb-tooth electrode 326 a through the plug330 d shown in FIG. 16, the middle layer 333 b of the outer frame 330,the torsion bar 362, the middle layer 324 b of the inner frame 320, andthe plug 320 e.

With electric potential applied to the comb-tooth electrode 311 a of themirror 310, when electric potential is applied to the comb-toothelectrode 325 a in the inner frame 320, electrostatic attraction orelectrostatic repulsion is generated between the comb-tooth electrode311 a and the comb-tooth electrode 325 a. Likewise, with electricpotential applied to the comb-tooth electrode 311 b in the mirror 310,when electric potential is applied to the comb-tooth electrode 326 a inthe inner frame 320 a, electrostatic attractive force or repulsive forceis generated between the comb-tooth electrode 311 b and the comb-toothelectrode 326 a. By means of these electrostatic forces, or acombination of these electrostatic forces, the mirror 310 rotates aroundthe rotating axis A3, as twisting the paired couplers 340.

On the other hand, with electric potential applied to the comb electrode321 a in the inner frame 320, when electric potential is applied to thelower layer 335-comb electrode 335 a in the outer frame 330,electrostatic attractive force or electrostatic repulsive force isgenerated between the comb electrode 321 a and the comb electrode 335 a.Likewise, with electric potential applied to the comb electrode 321 b inthe inner frame 320, when electric potential is applied to the lowerlayer 337 in the outer frame 330 or the comb-tooth electrode 337 a,electrostatic attractive force or electrostatic repulsive force isgenerated between the comb-tooth electrode 321 b and the comb-toothelectrode 337 a. By means of the electrostatic force or the combinedforce of the electrostatic forces, the inner frame 320, together withthe mirror 310, is rotated about the rotating axis A4 as twisting thepaired couplers 350 and 360.

In the micro-mirror element X3, the above-described drive mechanismactuates the mirror 310 and the movable unit including the inner frame320 to cause the mirror surface 313 of the mirror 310 to be directed inthe desired direction. Thus, with the micro-mirror element X3, it ispossible to change the direction of light reflected on the mirrorsurface 313.

In the micro-mirror element X3, the two torsion bars 351, 352 of thecoupler 350 are electrically separated from each other. The torsion bars351, 352 being mutually offset, the inner frame 320 and the outer frame330, to which the torsion bars are connected, are formed with aconduction path in a manner such that no short-circuiting occurs betweenthe torsion bars 351 and 352. At the same time, the two torsion bars 361and 362 of the coupler 360 are electrically separated from each other.As a result, the torsion bars 351, 352 are spaced from each other, andthe inner frame 320 and the outer frame 330 are provided with conductionpaths that cause no short-circuiting to occur between the torsion bars361 and 362. Owing to this, in the micro-mirror element X3, it ispossible to provide a plurality of potential-transmitting ways betweenthe outer frame 320 and the movable unit, whereby different potentialscan be applied simultaneously to the movable unit. With such anarrangement, the micro-mirror element X3 is provided with a high degreeof freedom in relation to the state of driving the movable unit,including the mirror 310 and the inner frame 320, and therefore complexoperations in the movable unit can be realized. As a result, themicro-mirror element X3 appropriately functions as a dual axis typemicro-mirror element.

The coupler 340 of the micro-mirror element X3, in the same manner asdescribed with relation to the coupler 113 of the micro-mirror elementX1, has a small twist resistance, while being capable of preventing themirror 310 from unduly rotating around its normal N3. Likewise, thecouples 350, 360 each have a small twist resistance, while being capableof preventing the inner frame 320 and hence the mirror 310 from undulyrotating about its normal N3.

Further, the micro-mirror element X3 is provided with a pair ofcomb-tooth electrodes 311 a and 325 a as well as a pair of comb-toothelectrodes 311 b and 326 a for the purpose of driving the mirror 310.Along with this, the micro-mirror element X3 is provided with a pair ofcomb-tooth electrodes 321 a, 335 a as well as a pair of comb-toothelectrodes 321 b, 336 a for the purpose of driving the inner frame 320.As in the above-described micro-mirror element X2, the comb-toothelectrode mechanism is appropriate for driving the movable unit with ahigh degree of precision.

1. A micro-actuation element comprising a movable unit, a support frameand a coupler for connecting the unit and the frame, the unit, the frameand the coupler being integrally formed in a material substrate with amulti-layer structure comprising a plurality of electroconductive layersand insulation layers arranged between the electroconductive layers, theelectroconductive layers including a core conduction layer, the movableunit comprising a first structure originating in the core conductionlayer, the frame comprising a second structure originating in the coreconduction layer, the coupler comprising a plurality of electricallyseparated torsion bars originating in the core conduction layer andcontinuously connected to the first structure and the second structure.2. The micro-actuation element according to claim 1, wherein the couplerincludes two torsion bars spaced from each other in a width direction,the two torsion bars having spacing that becomes greater as the bars arecloser to the movable unit.
 3. The micro-actuation element according toclaim 2, wherein inequalities 0<Wf<L and Wf<Wm<Wf+4L are satisfied,where Wf is spacing at the frame, Wm is spacing at the movable unit, andL is a distance between the movable unit and the frame at a position ofthe coupler.
 4. The micro-actuation element according to claim 1,wherein the movable unit comprises a movable core portion, a relay frameconnected to the support frame by the coupler, and a relay couplerconnecting the movable core portion and the relay frame.
 5. Themicro-actuation element according to claim 4, wherein the movable coreportion comprises a third structure originating in the core conductionlayer, the relay frame including the first structure, the relay couplerincluding a plurality of electrically separated torsion bars thatoriginate in the core conduction layer and are connected continuously tothe third structure and the first structure.
 6. The micro-actuationelement according to claim 4, wherein the relay coupler includes tworelay torsion bars spaced in a width direction, the two relay torsionbars having spacing that becomes greater as the bars are closer to themovable core portion.
 7. The micro-actuation element according to claim1, wherein the movable unit includes a first comb-tooth electrode, theframe including a second comb-tooth electrode for moving the movableunit by electrostatic force generated in cooperation with the firstcomb-tooth electrode.
 8. The micro-actuation element according to claim4, wherein the movable core portion includes a first comb-toothelectrode, the relay frame including a second comb-tooth electrode formoving the movable core portion by electrostatic force generated incooperation with the first comb-tooth electrode.
 9. The micro-actuationelement according to claim 1, further comprising a base facing themovable unit, wherein the base is provided with a flat electrode facingthe movable unit.
 10. The micro-actuation element according to claim 9,wherein the movable unit is provided with a flat electrode facing theflat electrode formed on the base.
 11. The micro-actuation elementaccording to claim 1, further comprising a base facing the movable unit,wherein the movable unit is provided with a first electromagnetic coil,the base being provided with a second electromagnetic coil or a magnetfor moving the movable unit by electromagnetic force generated incooperation with the first electromagnetic coil.
 12. The micro-actuationelement according to claim 1, further comprising a base facing themovable unit, wherein the movable unit is provided with a magnet, thebase being provided with an electromagnetic coil for moving the movableunit by electromagnetic force generated in cooperation with the magnet.13. The micro-actuation element according to claim 1, wherein themovable unit further includes a third structure originating in anelectroconductive layer connected to the core conduction layer via theinsulation layer in the material substrate, and wherein at least a partof the third structure and a part of the first structure are connectedto each other via a conduction plug passing through the insulation layerintervening between the third and the first structures.
 14. Themicro-actuation element according to claim 1, wherein the frame furtherincludes a third structure originating in an electroconductive layerconnected to the core conduction layer via the insulation layer in thematerial substrate, and wherein at least a part of the third structureand a part of the second structure are connected to each other via aconduction plug passing through the insulation layer intervening betweenthe third and the second structures.
 15. The micro-actuation elementaccording to claim 1, further comprising a mirror provided on themovable unit, wherein the element serves as a micro-mirror element. 16.A micro-actuation element comprising a movable unit, a support frame anda coupler for connecting these, the unit, the frame and the couplerbeing integrally formed in a material substrate having a multi-layerstructure that includes a first electroconductive layer, a secondelectroconductive layer, a third electroconductive layer, a firstinsulation layer intervening between the first and the secondelectroconductive layers, and a second insulation layer interveningbetween the second and the third electroconductive layers, the movableunit including a first structure originating in the secondelectroconductive layer, the frame including a second structureoriginating in the second electroconductive layer, the coupler includinga plurality of electrically separated torsion bars that originate in thesecond electroconductive layer and are continuously connected to thefirst structure and the second structure.
 17. The micro-actuationelement according to claim 16, wherein the movable unit further includesa third structure originating in the first electroconductive layer, andwherein at least a part of the third structure and a part of the firststructure are connected to each other by a conduction plug passingthrough the first insulation layer intervening between the third and thefirst structures.
 18. The micro-actuation element according to claim 16,wherein the movable unit includes a movable core portion, a relay frameconnected to the support frame by the coupler, and a relay couplerconnecting the movable core portion and the relay frame, the movablecore portion including a third structure originating in the firstelectroconductive layer and a fourth structure originating in the secondelectroconductive layer, at least a part of the third structure and atleast a part of the fourth structure being connected to each other by afirst conduction plug passing through the first insulation layerintervening between the third and the fourth structures, the relay framefurther including a fifth structure originating in the firstelectroconductive layer, the first structure originating in the secondelectroconductive layer and a sixth structure originating in the thirdelectroconductive layer, at least a part of the fifth structure and apart of the first structure being connected to each other by a secondconduction plug passing through the first insulation layer interveningbetween the fifth and the first structures, another part of the firststructure and at least a part of the sixth structure being connected toeach other by a third conduction plug passing through the secondinsulation layer intervening between the first and the sixth structures,the relay coupler including a plurality of electrically separatedtorsion bars that originate in the second electroconductive layer andare connected continuously to the fourth structure and the firststructure.
 19. The micro-actuation element according to claim 16,wherein the frame further includes a third structure originating in thefirst electroconductive layer and a fourth structure originating in thethird electroconductive layer, at least a part of the third structureand a part of the second structure being connected to each other by afirst conduction plug passing through the first insulation layerintervening between the third and the second structures, another part ofthe second structure and at least a part of the fourth structure beingconnected to each other by a second conduction plug passing through thesecond insulation layer intervening between the second and the fourthstructures.
 20. A micro-actuation element comprising a movable unit, aframe and a coupler connecting these, the unit, the frame and thecoupler being integrally formed in a material substrate having amulti-layer structure that includes a first electroconductive layer, asecond electroconductive layer, a third electroconductive layer, a firstinsulation layer arranged between the first and the secondelectroconductive layers, and a second insulation layer arranged betweenthe second and the third electroconductive layers, the movable unitincluding a first structure originating in the first electroconductivelayer, a second structure originating in the second electroconductivelayer and a third structure originating in the third electroconductivelayer, at least a part of the first structure and a first part of thesecond structure being connected to each other by a first conductionplug passing through the first insulation layer intervening between thefirst and the second structures, a second part of the second structureand at least a part of the third structure being connected to each otherby a second conduction plug passing through the second insulation layerintervening between the second and the third structures, the frameincluding a fourth structure originating in the first electroconductivelayer, a fifth structure originating in the second electroconductivelayer and a sixth structure originating in the third electroconductivelayer, at least a part of the fourth structure and a first part of thefifth structure being connected to each other by a third conduction plugpassing through the first insulation layer intervening between thefourth and the fifth structures, a second part of the fifth structureand at least a part of the sixth structure being connected to each otherby a fourth conduction plug passing through the second insulation layerintervening between the fifth and the sixth structures, the couplerincluding a first torsion bar that originates in the secondelectroconductive layer and is connected continuously to the first partof the second structure and the first part of the fifth structure, thecoupler also including a second torsion bar that originates in thesecond electroconductive layer and is connected continuously to thesecond part of the second structure and the second part of the fifthstructure.